1. Field of the Invention
The present invention relates to a film deposition method that deposits a thin film made of a reactive product by alternately exposing a substrate such as a semiconductor wafer to two or more kinds of reaction gases that react with each other.
2. Description of the Related Art
In recent years, high dielectric constant materials have been gradually used as an insulating layer of a memory cell in a semiconductor memory device. Among such materials, there is a zirconium oxide (ZrO). While the ZrO has a dielectric constant from about 24 to 40, there is a problem of having low voltage endurance. Therefore, as disclosed in International Publication No. 2008/108128 and Japanese Laid-open Patent Application Publication No. 2011-18707, using a ZrAlO film obtained by adding aluminum (Al) to the ZrO is tried to implement a high dielectric constant and high voltage endurance.
A film deposition method called an atomic layer deposition (ALD) method or molecular layer deposition (MLD) method is expected as a method of depositing the ZrAlO film, which is a ternary metallic oxide. According to the film deposition method, by repeating a ZrO cycle of depositing a ZrO film by alternately supplying a Zr-containing gas and an oxygen-containing gas to a substrate a plurality of times, and an AlO cycle of depositing an AlO film by alternately supplying an Al-containing gas and an oxygen-containing gas to a substrate a plurality of times, the ZrAlO film in which the ZrO film and the AlO film are alternately deposited can be deposited. In this case, composition of Al relative to Zr is determined by a ratio of an Al layer to a Zr layer. More specifically, the dielectric constant and the withstand voltage of the ZrAlO film are controlled by a ratio of the number of the Zr layer in the ZrO film deposited by the ZrO cycle to the number of the Al layer in the AlO film deposited by the AlO cycle.
As described above, in a case of controlling an Al composition (i.e., Al additive amount) by a layer number ratio of the Zr layer and the Al layer, the Al additive amount may not be controlled freely. For example, when the ZrAlO film contains four Zr layers in the ZrO film and one Al layer in the AlO film, a Zr0.8Al0.2O film is substantially deposited, and a Zr0.9Al0.1O film cannot be obtained. On the other hand, if nine Zr layers and one Al layer are provided in the ZrAlO film to deposit the Zr0.9Al0.1O film, a total film thickness of the ZrO film and the AlO film is forced to be thick, and so a thin ZrAlO film cannot be obtained according to conditions.